Explorations for oil and natural gas through geoseismic surveys continue to expand into the marine environment. A group of experts is calling for improved dialogue, legislation and planning at an international level, in order to ensure effective management of the potential risks threatening marine species.
As the name suggests, geoseismic surveys use seismic waves, analogous to those generated during an earthquake, to explore the structure and characteristics of the subsoil. Following technological advances and growing demand for fossil fuels, these explorations are now conducted throughout the year, at ever higher latitudes and in ever deeper waters. Particularly at risk is the Arctic, where the reduction in ice extent has opened up untapped potential for large-scale hydrocarbon exploration and extraction.
Due to the loud noise they introduce into the underwater environment and the effects they have on wildlife, geoseismic surveys have sparked considerable controversy. Numerous scientific studies show that as a result of these surveys marine animals can be driven away from their habitat, alter their behaviour, experience greater difficulty communicating, suffer high levels of stress and, if close to the noise source, sustain hearing damage. Such effects have been documented in marine mammals, but also in fish and invertebrates, meaning the entire food web could be affected. Thanks to its low frequencies, the noise can propagate across entire oceans, for hundreds or even thousands of kilometres.
A marine geoseismic survey is carried out using one or more vessels that typically deploy one or more air guns, which constitute the source of the seismic wave. When activated (usually once or twice per minute), the air gun releases a bubble of compressed air and generates a sound impulse directed downwards. As it travels through the water column and into the seabed, the acoustic wave is reflected and refracted by rock layers with different properties. The vessels also tow one or more receiver cables containing hydrophones (underwater microphones), which collect the reflected echo of the seismic wave. The characteristics of the echo and the time it takes to reach the receivers provide information about what the wave encountered in the seabed and yield a detailed image of its structure. Commercial geoseismic surveys are generally aimed at identifying subsea hydrocarbon basins, so that oil companies know exactly where they need to drill to extract resources. This type of survey is also used for research purposes to study the geophysical properties of the ocean floor.
A group of experts from various universities and organisations around the world has conducted a study published in Frontiers in Ecology and the Environment which highlights how, given the broad spatial and temporal scale over which noise generated by geoseismic explorations propagates, existing measures to assess, mitigate and monitor its potential consequences are, at best, inadequate. Protocols are neither standardised nor updated in line with the latest scientific findings on impacts and mitigation technologies, such as marine vibroseis, an alternative technology that could replace air guns. Furthermore, they do not take into account the cumulative and repeated exposure to which animals are subjected over time, which can cause long-term damage that is difficult to detect at a small scale.
The experts state that governments, scientists, environmental organisations and industries must work more closely together at regional and international level to promote more effective coordination in the management and planning of these activities. The European Union and other bodies have recognised noise as a form of pollution, but further international standards are needed that go beyond national and regional boundaries, for example through the revision of the International convention on the prevention of pollution from ships (Marpol). This would lead to the creation of standardised rules and protocols that would facilitate the assessment of potential impacts, the application of state-of-the-art mitigation strategies and the collection of important monitoring data.
Translated by Francesca Clemente